This proposal deals with the structure, expression, and functional role(s) of each of the six actin genes of the actin multigene family of Drosophila melanogaster. We propose to develop unique sequence cloned probes for the transcript of each actin gene from the transcribed, but nontranslated portion of the mRNA. These probes will be used to investigate the timing, transcript size, and possible hormonal triggering of the mRNA transcript from each actin gene by hybridization to "Northern" blots of polyA RNA from various stages of the D. melanogaster life cycle and certain mass isolated tissues, including neoplastic imaginal discs. We also propose to hybridize the gene-specific probes in situ to cytological sections of D. melanogaster ovaries, embryos, larvae, and adults to investigate the stage and tissue specificity of the transcriptional activity of each gene. Mutants at each actin locus will be selected in order to correlate the expression of a transcript with the funcional role(s) of its product in the organism. These experiments are designed to define the relationships between the individual members of the actin multigene family during development and in certain D. melanogaster neoplasias.